In order to be able to control the operation of household devices reliably and automatically, it is necessary to determine their operating states reliably and accurately. Thus, it is known for example in household devices such as for example washing machines, dishwashers and dryers to monitor the actual properties of fluids that are employed. In the case of washing machines and dishwashers the optical transmission of cleaning liquid is for example measured in order to determine the actual degree of cleanliness of objects to be cleaned and to appropriately control the operation. The same also applies to the drying air used in dryers.
Also, the measurement of fluid temperature and electrical conductivity can provide information on the actual operating state and establish a basis for how the operation should subsequently be controlled, in order for example to achieve an optimum cleaning result.
Known approaches have disadvantages as regards the measurement accuracy and reliability. Thus, for example, measurements can be affected on account of the operation of the household device and the measurement methods that are employed, with the result that the measurement results may be inaccurate and unreliable. Also, time-consuming and complex methods are normally required to evaluate the measurement values.